Doctor of Philosophy
Dr. Charles L. Rice
Recording motor unit (MU) action potentials during fast muscle contractions, specifically during movement, presents unique challenges that constrain the investigation of the upper limits of human MU performance. The anconeus muscle exhibits many advantageous characteristics that suggest it is an appealing model for the study of MU behaviour in challenging experiment paradigms. Thus, the purpose was to determine the MU recruitment and discharge properties associated with the generation of movement up to maximal angular velocities of elbow extension and to determine the effect of submaximal fatiguing movements on these MU properties. Due to the synergistic nature of the anconeus in the elbow extensor muscle group, a secondary purpose was to determine whether MUs of the muscles comprising the elbow extensor group behave differently during the production of high forces.
Discharge rates and recruitment thresholds were tracked in 24 and 17 MUs, respectively. It was revealed that anconeus MUs increase discharge rates over two distinct linear ranges possessing different input-output gain relationships relative to elbow extension velocity. Anconeus MUs exhibited variable responses to increased resultant velocity when recruitment thresholds were considered. These variable responses, that were more common in higher threshold MUs, indicated that a compression of the MU recruitment range of the anconeus occurred as elbow extension velocity increased.
Using the same recording techniques, fatigue-related changes in discharge rates and recruitment thresholds of 12 MUs were determined throughout a protocol comprised of fast, maximal, static muscle contractions, and submaximal and periodic maximal movements. Results of this study demonstrated that MU properties are graded differently in response to submaximal fatiguing movements depending on the intensity of the movement, but that contraction type did not affect the relative changes in these MU properties.
Lastly, MUs in three elbow extensors including the anconeus were tracked during constant joint angle force production to near maximal intensities. Differences between the elbow extensors were observed for MU discharge rates and recruitment thresholds with increasing force. These findings support an integrated model of earlier established MU control strategies for the elbow extensors and show anconeus MU recruitment occurs over a greater range than previously believed.
Harwood, Brad, "Task-Dependent Properties of the Human Anconeus Muscle" (2012). Electronic Thesis and Dissertation Repository. 844.